Traditional usage and biological activity of Plectranthus madagascariensis and its varieties: a review.

ETHNOPHARMACOLOGICAL RELEVANCE: Plectranthus madagascariensis (Pers.) Benth. is an indigenous aromatic South African plant species that are traditionally used to treat various dermatological and respiratory ailments. AIM OF THE STUDY: Three varieties of P. madagascariensis exist in South Africa, namely, Plectranthus aliciae (Codd) van Jaarsv. & T.J. Edwards, Plectranthus ramosior (Benth.) Van Jaarsv. and Plectranthus madagascariensis (Pers.) Benth var. madagascariensis. This article summarizes the documented ethnobotanical uses and research which has been conducted to date on the chemical constituents and biological effects of P. madagascariensis and its varieties. This review aimed to investigate and highlight the lack scientific reports of the potential activity of these varieties based on their traditional usage and to emphasise the need for further investigation of the benefits of P. madagascariensis and its varieties.
MATERIALS AND METHODS: Extensive database retrieval using platforms not limited to but including Google Scholar, ScienceDirect and PubMed, was performed by using keywords such as "Plectranthus madagascariensis" "Plectranthus madagascariensis var. aliciae", "Plectranthus aliciae", "Plectranthus ramosior", "Plectranthus madagascariensis var. ramosior" and "Plectranthus hirtus" In addition, relevant books and digital documentation were consulted to collect all available scientific literature to provide a comprehensive review.
RESULTS: Several studies have reported on the traditional usage of P. madagascariensis for the treatment of diseases related to the respiratory system such as coughs, colds and asthma and dermatological disorders related to wounds and inflammation. No records were found on the traditional usage of P. madagascariensis varieties to treat other maladies, however, P. ramosior has been reported to be used as a toxin for fishing. In literature, seven major phytochemical compounds have been identified in P. madagascariensis. Its extract and essential oil have been reported to have polyphenols, abietane diterpenes and abietane diterpenes with a quinone moiety as constituents. Plectranthus madagascariensis and its major phytochemicals have been reported to target various biological targets. The report on the antibacterial activity of P. madagascariensis against tuberculosis and wound infections has been consistent and correlates with its documented traditional usage of the plant. Literature has been found on the antibacterial activity of P. aliciae targeting bacteria associated with wound infections and lung cancer cells. No further literature on the biological activity of the other P. madagascariensis varieties has been found. Other noteworthy biological activities reported in the literature of P. madagascariensis and identified phytochemicals include their activities against Alzheimer's disease and cancer, especially against breast cancer and this has not been linked to the traditional usage of the plant.
CONCLUSION: Plectranthus madagascariensis and its compounds have been proven to be effective in treating a range of maladies. Based on the extensive literature on this plant, it can be concluded that numerous in vitro pharmacological activities of P. madagascariensis have been reported. However, there is a lack of information available for this species with regards to its in vivo data including both pre-clinical and clinical studies. Since the extract of P. madagascariensis and its isolated compounds have displayed noteworthy anticancer potential, we recommend further investigation of pharmacokinetic studies to be included in future research.